Support of X.21, X.21 bis and X.20 bis based Data Terminal Equipments (DTEs) by an Integrated Services Digital Network (ISDN)
This Recommendation is also included but not published in I series under alias number I.461

Interface between Data terminal Equipment (DTE) and Data Circuit-terminating Equipment (DCE) for terminals operating in the packet mode and accessing a Packet-Switched Public Data Network through a public switched telephone network or an Integrated Services Digital Network or a Circuit-Switched Public Data Network

Interface between data terminal equipment (DTE) and data circuit-terminating equipment (DCE) for terminals operating in the packet mode and connected to public data networks, designed for efficiency at higher speeds

Use of X.25 LAPB-compatible Data Link procedures to provide the OSI connection-mode Data Link service
This title results from the modification of ITU-T X.222 (04/95) former title by Amendment 1 (10/96).

[Withdrawn] Procedure for the exchange of protocol identification during virtual call establishment on Packet Switched Public Data Networks
Superseded by the more comprehensive description of protocol identifiers contained in X.263

General arrangements for interworking between Circuit-Switched Public Data Networks (CSPDNs) and Integrated Services Digital Networks (ISDNs) for the provision of data transmission services
This Recommendation is also included but not published in I series under alias number I.540

General arrangements for interworking between Packet-Switched Public Data Networks (PSPDNs) and Integrated Services Digital Networks (ISDNs) for the provision of data transmission services
This Recommendation is also included but not published in I series under alias number I.550

[Withdrawn] Message handling systems: conformance testing
This Recommendation was withdrawn because conformance testing concepts and methods defined in it were related to the 1984 MHS Recommendations and were not aligned with either the first or second versions of conformance testing standards. ITU-T X.480 (1992) refers to the 1988 "Blue Book" MHS Recommendations and was better aligned with the testing standards

[Withdrawn] Message handling systems: Abstract service definition conventions
This Recommendation was not referenced from any Recommendation and some of its technical content was contained in ITU-T X.402 (1995)